The present disclosure relates generally to powered, fastener-driving tools, wherein the tools may be electrically powered, pneumatically powered or powder activated, and more particularly to a combustion-powered fastener-driving tool having a trigger control mechanism that is operable in both a sequential actuation mode and a contact actuation mode.
Powered, fastener-driving tools of the type used to drive various fasteners, such as, for example, staples, nails, and the like, typically include a housing, a power source, a supply of fasteners, a trigger mechanism for initiating the actuation of the tool, and a workpiece contact element (also referred to herein as a “workpiece contacting element” or “WCE”). The workpiece contact element is configured to engage or contact a workpiece, and is operatively connected to the trigger mechanism, such that when the workpiece contact element is in fact disposed in contact with the workpiece, and depressed or moved inwardly a predetermined amount with respect to the tool, as a result of the tool being pressed against the workpiece a predetermined amount, the trigger mechanism is enabled to initiate actuation of the fastener-driving tool.
As is well-known in the art, powered, fastener-driving tools normally have two operational modes, and the tool is accordingly provided with some mechanism, such as, for example, a lever, a latch, a switch or the like, for enabling the operator to optionally select one of the two operational modes that the operator desires to use for installing the fasteners. More particularly, in accordance with a first one of the operational modes, known in the industry and art as the sequential or single-actuation mode of operation, the depression or actuation of the trigger mechanism will not in fact initiate the actuation of the tool and the driving of a fastener into the workpiece unless the workpiece contact element is initially depressed against the workpiece. Considered from a different point of view or perspective, in order to operate the powered, fastener-driving tool in accordance with the sequential or single-actuation mode of operation, the workpiece contact element must first be depressed against the workpiece followed by the depression or actuation of the trigger mechanism. Still further, once the particular fastener has in fact been driven into the workpiece, further or repeated depression or actuation of the trigger mechanism will not result in the subsequent driving of additional fasteners into the workpiece unless, and until, the workpiece contact element is permitted to effectively be reset to its original position and once again disposed in contact with, and pressed against, the workpiece prior to the depression or actuation of the trigger mechanism each time the tool is to be actuated so as to drive a fastener into the workpiece.
Alternatively, in accordance with a second operational mode, known in the industry and art as the contact actuation mode of operation, the operator can in fact maintain the trigger mechanism at its depressed position, and subsequently, each time the workpiece contact element is disposed in contact with, and pressed against, the workpiece, the tool will actuate, thereby driving a fastener into the workpiece.
Combustion-powered tools are known in the art. Exemplary tools are manufactured by Illinois Tool Works, Inc. of Glenview, Ill. for use in driving fasteners into workpieces, and are described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452 and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722; 5,133,329; 5,197,646; 5,263,439; 6,145,724 and 7,383,974, all of which are incorporated by reference herein.
Such tools incorporate an external tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and a fan located in a combustion chamber provides for both an efficient combustion within the chamber, while facilitating processes ancillary to the combustion operation of the device. Such ancillary processes include: cooling the engine, mixing the fuel and air within the chamber, and removing, or scavenging, combustion by-products. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a single cylinder body.
A valve sleeve is axially reciprocable about the cylinder and, through a linkage, moves to close the combustion chamber when the workpiece contact element at the end of the linkage is pressed against a workpiece. This pressing action also triggers a fuel-metering valve to introduce a specified volume of fuel into the closed combustion chamber. This same movement of the tool against the workpiece causes the fan inside the combustion chamber to turn on and mix the fuel with the air inside the combustion chamber.
Upon the pulling of a trigger, which closes a trigger switch, a spark is generated for igniting a charge of gas in the combustion chamber of the engine, the resulting high pressure inside the chamber causes the combined piston and driver blade to be forced downward to impact a positioned fastener and drive it into the workpiece. Just before the piston impacts a resilient bumper at a lower end of the cylinder, the piston passes an exhaust port, through which some of the exhaust gas is vented. Next, the tool valve sleeve and cylinder absorb heat from the combustion to generate vacuum pressure that pulls the piston back to its uppermost position in the cylinder for the next cycle. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
For efficient operation, it is preferred that the combustion chamber remains sealed until the piston returns to its uppermost or pre-firing position. The amount of time that the combustion chamber remains closed is a function of the operator's work rhythm and is often too short when attempting a repetitive cycle operation, where the trigger remains pulled and the workpiece contact element is rapidly pressed upon the workpiece for fastener driving, and then the tool is quickly lifted and moved to the next fastener location.
In cases where a tool is operated at a much higher cycle rate, the operator can open the combustion chamber during the piston return cycle by removing the tool from the workpiece. This causes the vacuum to be lost, however, and piston travel will stop before reaching the top of the cylinder. This leaves the driver blade in the guide channel of the nosepiece, thereby preventing the nail strip from advancing towards the nose. The net result is no nail in the firing channel and no nail fired in the next shot.
To assure adequate closed combustion chamber dwell time in the sequentially-operated combustion tools identified above, a chamber lockout device is known that is linked to the trigger. This mechanism holds the combustion chamber closed until the operator releases the trigger. This extends the dwell time (during which the combustion chamber is closed) by taking into account the operator's relatively slow musculature response time. In other words, the physical release of the trigger consumes enough time of the firing cycle to assure piston return. The mechanism also maintains a closed chamber in the event of a large recoil event created, for example, by firing into hard wood.
Conventional combustion-powered fastening tools typically operate in the sequential actuation mode. As a result, experienced carpenters typically use the sequentially actuated combustion tool for precision nailing and a different contact actuated tool for non-precision nailing, such as for roofing and decking. A need therefore exists for a single combustion fastener-driving tool that is operable in both a sequential actuation mode and a contact actuation mode.